Electric power system



Sept. 20,1927. J J KANE 1,643,213

' ELECTRIC POWER SYSTEM Filed Oct. 14, 1920 Patented Sept. 20, 1927.

UNITED STATES JOHN J. KANE, 0F MILWAUKEE, WISCONSIN, ASSIGNOR TOALLIS-CHALMERS MANU- PATENT OFFICE.

FACTURING COMPANY, OF MILWAUKEE, WISCONSIN, A CORPORATION OF DELA- WARE.

ELECTRIC POWER SYSTEM.

Application filed October 14, 1920.

This invention relates in general to electrical power and distributionsystems, and has particular relation to devices or appaatus forregulating generators driven by prime movers, such as engines orturbines connected to supply variable electrical loads, especially wherethere is a tendency for the generator-driving means to operate at aspeed dependent upon the load.

In certain installations, as where a steam turbine drives a generator,usually through a direct connection therewith, for supplyinga variableelectrical load, such as lights on a railway train or the locomotivethereof, means are necessary for regulating or limiting the speed of theturbine on the loss of a portion of the generator load, and also on anappreciable increase in the steam pressure at the turbine inlet. It willbe obvious, that, if the generator were permitted to operate at agreatly increased speed on the removal of a portion of its normal loador an increase in pressure at the turbine inlet, the voltage on thelamps or othertranslating devices constituting the load on the generatormight rise to a dangerously high value, and this is especially the casewhere the load comprises lamps of the incandescent type, whereacomparatively small voltage variation may be highly injurious to thelife of the lamps. Again, unless some means is.

provided for effectively limiting the speed of the generator andtheturbine driving the same to a safe operating value on the removal ofgenerator load, there is liable to be unnecessary wear and strain uponthe generator and turbine, and even considerable danger to theseelements of the system.

In accordance with this invention, improved means are provided forregulating the speed of the prime mover and the speed and outputof thegenerator, the means disclosedherein constituting a modification of themeans for the same general purpose disclosed in applicants copendingapplication Serial No. lQJOhfiled July 2st. 1915, and an object of theregulating means provided herein is to maintain a characteristic, suchas the voltage, of the energy supplied by the generator substantiallyconstant independently'of the speed thereof or of any tendency of taeprime-mover to operate at a variable speed dependent upon the load onthe generator, while at the same timcholding the speed of the generatorand its driving means,

Serial No. 417,004.

within alimiting value at which these elements can operate continuouslywithout any harmful effects. For this regulating purpose, an artificialload is provided which takes the place of at least a portion of theelectrical load removed from the generator circuit, the regulation beingeffected in re sponse to variations in the speed of the generator andits driving means, this manner of regulating the set involvingconsiderable economy as to power used for braking purposes, especiallywhen there is a substantial load on the generator; and it also has thedesirable feature that the power rating of the generator or theprime-mover need not be appreciably greatertha-n is necessary to supplythe normalor full electrical load on the generator.

It is an object of this invention to provide a system comprising amachine supplymg a load of a variable, character, and improved means forcontrolling said machine as desired independently of the load on themachine, while confining the speed of the machine to a desired safeoperating value.

lt is a further object of this invent-ion to provide a system ofdistribution comprising a generator supplying a load ofa'variable-character and driven by fluid-operated means whichautomatically tends to increase its speed on loss of load, and improvedmeans for maintaining the voltage of the generator substantially-'constant or within a desired limitindependently of the load on the generator, while at the same time confining the speed of the generator andits driving means to a desired limiting value.

it is a further object of this invention to provide for a system of thecharacter described improved regulating apparatus comprising anelectrically operative brake, and means for effectively energizing thebrake to a degree responsive to the speed of the generator and itsdriving means.

These and other objects and advantages are attained by this invention,the various novel features of which will appear from the description anddrawings, disclosing one or more embodiments of the invention, and willbe particularly pointed out in the claims.

In the accompanying drawings;

Fig. l is a diagrammatic showing of a system involving features of thisinvention.

Figs. 2 and arediagrammatic views showing modifications of the system ofFig. 1. i

In the embodiment of the invention disclosed in Fig. 1, a generator G isdriven by a prime mover, such as a steam turbine T which is preferablymounted on the generator shaft. The shunt field of the generator isindicated at 11 and the series field at 12, the machine terminals beingconnected to the distribution circuit a, Z), which supplies a number ofelements of a variable load L which may be considered as a lamp load.The turbine T is provided with an inlet 13 of adjustable size, although,in the ordinary operation of the system, the inlet opening usuallyremains constant when adjusted, this adjustment depending upon thenormal generator speed desired under conditions of full load on thegenerator, and the working pres sure of the steam at the turbine inlet.This pressure may be considered as being main tained substantiallyconstant, as by means of a reducing valve, or otherwise. A brake B isprovided,-the same being designed to act as an artificial load on theshaft of the gen: erator and turbine, this brake comprising a disk 14 ofconductive material mounted on the shaft and rotatable between poles ofan electromagnetic field element 15.

As mentioned above, the turbine T is of a character such that, with adefinite throttle setting and inlet pressure, the speed thereol tends tovary inversely as the load. While the system of Fig. 1 contemplates somevariation in the speed of the turbine and generator, nevertheless, thebrake B and its energizing means are of a character to limit this speedvariation to a desired extent, this permissible speed variation beingutilized to cause the load on the turbine to be of such. a value asinsures maintaining the speed within the desired limit at all times.

lVhile the regulation of the generator field so as to securesubstantially constant voltage in spite of speed variations may besecured to a greater or less degree, as desired, through the cumulativeseries winding 12, nevertheless, a voltage-responsive regulating devicemay be provided in addition. This additional regulator may comprise aresistance 17 in shunt to the field 11, the circuit through theresistance being normally open and being closable by an oscillatingswitch or circuit-closer 18 actuable by a voltageresponsive magnet 19 tomaintain the gen erator voltage substantially constant. This voltageregulating means acting on the shunt field may, initself, be sufiicientto maintain constant voltage without the series field.

T The electromagnetic field element 15 com-- prises two spaced polarportions, as indicated, in the air-gap between which the conductive disk14 is rotatable. The magnetic circuit around the air-gap is closedthrough two parallel paths, the path 21 being of relatively reducedcross-sectional area so as to provide for its magnetic saturation underpredetermined conditions of operation, and the path 23 being of normalcross-sectional area, that is, being unsaturable under any ordinaryoperating conditions. The field element is energized by winding 24: diposed upon the unsaturable portion 23 of the magnetic circuit. Thiswinding 24: is supplied from an exciting magneto or generator M,preferably mounted upon the shaft of the turbo-generator, and in anycase being so arranged that its speed varies directly as the speed ofthe turbine. As indicated, this magneto is self-excited by a shunt fieldwinding VJith such an arrangen'ient, the voltage at the magnetoterminals, and hence the energizing efiect produced by the winding 24,varies directly as the speed of the magneto and the turbine driving thesame; and, due to the fact that the windin 25 is of the shunt type andsupplied from the magneto terminals, there are two variable elementswhich operate to increase the voltage of: the magneto as the speedthereof in creases. In other words, there is an increase in voltage dueto increase in speed and a :turther increase due to the increasedenergizing efiiect of the winding 25. This increase in voltage at theterminals of the mag neto M, during the predetermined speed va riationof the turbine that is present between the upper and lower limits ofload on the generator G, isutilized for varying the retarding efiect ofthe brake B, this braking effect being such as takes the place oi thegreater portion of the load removed from the circuit of the generator GAssume that the system is operating under conditions of normal or fullelectrical load on the generator G. At this time,tl rough the efi'ect ofthe shunt winding 11, with its voltage-responsive regulator and theseries winding 12, the generator voltage is maintained constanteventhough there may be slight variation in the speed of the turbine andgenerator. At this time, the magneto M, being excited by its shuntwinding 25, is operative to excite the winding 2% only to a degree.sufiicient to cause the latter to pro duce an amount of magnetic fiuxthat approximately saturates the shunt path 21. Under these conditionsoi operation, substantially all of the flux generated in the path 23015the electromagnet threads the path 21, only a comparatively small andineffective portion of the total fiux passing across the air-gap of themagnet and through the conductive disk Ll. Under these conditions ofoperation, the brake B exerts no appreciable braking efiect upon theturbine shaft.

Assume now that a portion of the lamp load is removed from the generatorcircuit. The eifect of this loss in generator load is to Sif) cause theturbine and generator to speed up, the regulator 19 along with theseries winding 12 being sufficient to maintain the voltage on thegenerator the same as existed under conditions of full load. On increasein the speed of the turbine shaft, the speed of magneto M increases, theeffect thereof being a considerably increased voltage at its terminals,this voltage increase bein reflected in the increased energization ofthe winding 2 In view of the fact that the path 21 of the electromagnet15 was saturated at the voltage produced by the magneto under conditionsof full load on the generator G, the increased voltage of the magneto isutilized substantially wholly in producing flux that passes across theair-gap and through the conductive disk 14, thus producing a brakingeffect upon the turbine shaft which is sufficient to hold the speedincrease to a value considerably lower than what it would be were thisbraking arrangement not provided.

As the load on the generator decreases to zero, the voltage at thegenerator terminals is maintained constant and there is a con tinualincrease in speed of the turbo-generator and the magneto M. Thisincrease in speed causes an increase in the voltage of the magneto toits maximum value, predetermined by the design thereof and the maximumspeed desired under conditions of no load on the generator G, and thereis a consequent increased braking effect exercised by the brake B, thusholding down the speed of the turbine to a desired limiting value.

It will be apparent that, as the electrical load is removed from thegenerator, there is substituted therefor as an effective load upon theturbine, an increase in the load due to the magneto M, an increase inthe braking effecton the turbine shaft due to the brake B, and also anincrease in the windage loss of the various rotating elements due to thehigher operating speeds. These losses may be substantially theequivalent of the load removed from the generator circuit, so that itmay be considered that there-is a fairly constant total load ontheturbine at all times.

By proper design of the generator, the magneto M, and the brake B, theincrease in the turbine speed between that corresponding to full load onthe generator and no load thereon, may be limited to a relatively smallamount say from 10% to 25% or even less, of the full load speed. EVdesigning the system so that this permissible speed variation isutilized for controlling the regulation of the system, a minimum size ofgenerator and turbine may be utilized, for the generator losses forbraking purposes under conditions of full load on the generator are aminimum, as distinguished from certain prior art apparatus where thetotal energy supplied to the brake is a maximum under conditions of fullload upon the generator, thus requiring greater capacity or power ratingof the generator and turbine.

It will be apparent that the magneto M, may, if desired, be excited fromany desired source, such as a battery or the terminals of the generatorG. Likewise, under conditions of separate excitation, the magneto mayreadily be ofv alternating current type.

In the system disclosed in Fig. 2, the generator may be the same as thatof Fig. l, as shown, or the series winding may be omitted and the shuntwinding with its regulator may be relied upon wholly to maintainconstant voltage upon the generator circuit. In order to decrease theamount of power consumed by the brake B under conditions of normal orfull load on the generator, the

system is so designed that the magneto M does not furnish anyappreciable power to the brake when the'speed of the set is below thatcorresponding to full load on thegenerator; and the field of'the brakemay be in the form of a simple magnetic element 31 having an air-gapbetween opposed polar portions, and the energizing winding 24.

As an additional element in controlling the voltage of the generator G,there is provided afield winding 32 supplied from the terminals of themagneto M, this field Winding being designed to oppose the energizingeffects produced by the voltage and series windings. Thus as load isremoved from the generator and the speed thereof consequently rises,this winding 32 has an increasing effect in reducing the effective fieldexcitation of the generator, thus assisting in holding down the voltagethereof in spite of variations in speed.

During operation of the set at speeds up to the value corresponding tonormal or full load upon the generator G, the winding 24 may besubstantially unenergized, there being no requirement at this'tinie forthe exercising of a braking effect upon the furbine shaft. This resultor operationmay be secured by having the circuit of the magneto M,either the armature or the field circuit, open at this time. In theparticular embodiment'of the invention shown. the armature circuit ispermanently closed through the winding 24, and the field circuit 25 isnormally open and is closable by a switch element which is actuatedthrough a speed responsive device Cassociated with the armature of themagneto or the turbine shaft. the'switch element being operable throughan element 36 when the speed of the turbine rises to a point slightlyabove that corresponding'to full load upon the generator. In otherwords, as a portion of the generator load is removed, causing anincrease in speed of the turbocess speed thereof.

generator above normal, the centrifugal device C becomes effective toclose the circuit of field winding 25, and thus render the brake B moreor less effective, depending upon the voltage of the magneto M, for thepuroose of braking the turbine shaft. As described in connection.witlrthe system of Fig. 1. during operation at speeds corresponding togenerator loads between full and zero values, the braking effectexercised by the brake B of Fig. 2 varies directly as the turbine speed.

The voltage on the generator G may be readily maintained constant by themeans described during the variation in load on the generator. and theincidental variation in speed of the set may be limited to any desiredamount, say 15%, this variation in speed being utilized for effectingthe desired control of the turbine to prevent eve In accordance with thedisclosure of 3, the brake B is of the same form as that of the systemof Fig. 2, and the generator G is provided with both shunt and serieswindings, as shown in Fig. 1, and also with a bucking winding 82, asshown in Flg. 2, the latter winding being supplied by the magneto M.

In order to provide economy in the amount of power utilized. that is, tofurther reduce the required total power or rating of the turbine T underconditions of normal or full load on the generator G, the field elementat of the magneto M may be of a special type. As shown, the armature ofthe magneto operates between spaced polar portions which are connectedby parallel magnetic paths 4L2 and 43. The path L3 is of reducedcross-sectional area so that it may readily become magneticallysaturated under certain operating conditions, while the path 42 is ofnormal cross-sectional area and is designed to remain unsaturated underany ordinary operating conditions. The main path 42 is excited by awinding 45 supplied from a separate exciter E, preferably mounted uponthe turbine shaft, and a shunt winding 46, preferably superposed on thewinding 45 and supplied from the terminals of the magneto M. The exciterE may have a field winding supplied from a separate source, such as thegenerator G, or a shunt winding 52, or both windings.

Under conditions of full load on the generator G, substantially all theflux produced by the winding 45 returns through the path a3, and noeffective flux passes through the air-gap and the armature of themagneto; and thus, no effective voltage is produced at the terminals ofthe magneto. As the generator load is reduced, and consequently thespeed of the turbine is increased, the magnetic flux produced by thewinding 4-5 is sufficient to create an appreciable flux across theair-gap of the field element and the 'arn'iature of the magneto, rceultithe production of a substantial voltage at the magneto terminals. Thewinding 46 is thus rendered effective to produce flux which iscumulative relative to the flux produced by the winding d5, thus forcingr greater and greater amount of flux to pass through the armature of themagneto. The general effect is to cause the winding Q-l of the brake Bto produce a substantial energizing effect upon the brake, and thuscause the exertion of a substantial braking effect by the latter. As theload on the generator varies and the speed thereof eonsequently varies.the effective voltage at the terminals of the magneto M and theretarding effect of the brake is accordingly varied, the general effectbeing the maintenance of the required load on the turbine T to preventthe speed the latter from rising beyond a predetermined safe value.

It will. be apparent that by proper de sign of the various elements ofthese sys temsthe eesired braking effect may be produced on the turbineT to hold the speed of the latter within any desired limits duringvariation of the generator load from zero to its maximum value. Further,there is a minimum loss of power for braking purposes when the load onthe generator maximum. this resulting in that the gen erator and turbinemay be of minimum size to take care of the maximum electrical loadrequirements of the system. Again, the de sired regulation of the systemmay e cured Without the necessity of controlling devices havingrelatively movable parts that may need adjustment or may get out oforder.

It will be apparent from the disclosure as to the various systemsdescribed above, that in each case there is provided system involving aprime mover whose speed tends to vary in accordance with the loadthereon and supplying a generator or other variable load, andautomatically-acting means for insuring effective limitation of thespeed of the turbine to a safe operating value under all conditions ofload on the generator or equivalent element of the system. Further, itwill be apparent that this control of the driving element is secur l independently of the electrical circuit of the generatoror other drivenelement, the permissible speed variation alone being utilized to securethe desired regulation of the sys tem. It will be further apparent tha"a system is provided wherein a prime mover drives a generator supplyinga variable load, and the voltage of the generator is maintainedsubstantially constant independently of variations in the load thereon,and the speed of the turbine is limited to a safe ill operating valueunder all conditions of generator load.

law

It should be understood that it is not desired that the inventionclaimed be limited to the exact details of construction shown anddescribed, for obvious modifications will occur to a person skilled inthe art. I

It is claimed and desired to secure by Letters Patent: I i i 1. Incombination, a generator having means for maintaining the voltagethereof substantially constant in spite of variations in the generatorspeed, means for driving said generator, an electromagnetically-actuatedbrake for said generator-driving means, and means for effectivelyenergizing said brake to a degree that varies as the speed of saidgenerator. 7

2, In combination, a generator having means for maintaining the voltagethereof substantially constant in spite of variations in the generatorspeed, means for driving said generator, an electromagnetically actuatedbrake for said generator-driving means, energizing means for said brake,and speedresponsive means for causing the effective energization of saidbrake to vary from a minimum When the generator is operating at a speedcorresponding to full load thereon to a maximum When the generator isoperating at a speedcorresponding to no load thereon.

3. In combination, a generator having means for maintaining the voltagethereof substantially constant in spite of variations in the generatorspeed, means for driving said generator, an electromagnetically-actuatedbrake for said'gencrator driving means, and energizing means for saidbrake, said energizing means comprising a source of electrical energyWhose voltage varies as the speed of said generator and operative tocause the efiective energization of said brake to vary directly as thespeed of said generator.

4. In combination, a generator having means for maintaining the voltagethereofsubstantially constant in spite of variations in the generatorspeed, means for driving said generator, an electromagneticallynctuatedbrake for said driving means,and energizing means for said brake,operative to cause the braking effect thereof to vary directly as thespeed of said generator said energizing means comprising an energizingwinding for the brake, and a shunt-Wound,

variable voltage source of energy for supplying said Winding.

5. In combination, a compound-Wound, constant voltage generator, meansfor driving said generator, an electromagnetically actuated brake forsaid generator-driving means, and energizing means for said brake forcausing the energizing effect of said brake to vary directly as thespeed of said generator and its driving means, said energizing meanscomprising a variable voltage source of electrical energy,

6. In combination, a primeinover having a tendency to operate at a speeddependent upon its load, a generator driven thereby and having means formaintaining its voltage substantially constant in spite of variations inspeed, an electromagnetically-actuatcd brake for said prime-mover, andenergizing means for said brake eifective to insure the production; ofno appreciable brak-. ingetfect While the speed of said generator isbelow that corresponding tofullgenerator load and to cause theproduction of a braking eifect that varies as the speed of saidgenerator for generator speeds above that corresponding tofullg-eneratonload, said energizing means comprising an electromagneticdevice including a saturable magnetic path.

7. In combination, a constant voltage generatorhaving a differentialfield Winding, a 55 separate source ofvariablevoltage for energizingsaid differential field Winding, means for driving said generatoran'dsaid separate source, and means for producing a braking 'efiect on saidgenerator-driving means that 9" varies directly as the speed of saidgenerator and its driving means, said means jcompris ing anelectromagnetically-actuated brake for said generator-driving means. 7

8. In combination, ,a. generator, means for preventing the voltage ofsaid generator from varying directly as the speed thereof and comprisinga differential field Winding, a separate source of variable voltage forsupplying said ditterential inding, means for driving said generator andsaid separate source, an electromagnetically-actuated brake for saidgeneratondriving means, and anenergizing Winding for said brake suppliedfrom said separate source, said separate 1 source including energizingmeans efiective' to cause the voltage of said separate source tobe'substantiallyzero When said generator isoperating ataspeedcorresponding to full load on said generator and to vary directly as thespeed of the speeds thereof. i a

9. In combination, a constant voltage generator, having a differentialfield Winding supplied from a separate source of variable voltage,avariable'speed driving means for said generator, anelectromagnetically-actuated brake for said generator-driving means, andenergizing means for saidxbrake operable generator for all highertoflinsure. the production of no appreciable braking effect while thespeed ofsaid generator corresponds to full load thereon and to cause theproduction of a braking elfect that varies as the speed ofsai'dgenerator for speeds thereof above that corresponding to full load, saidenergizing means comprising a magnetic ,device having a saturablemagnetic'path, and said differential windingbeing ineffective to causeappreciable influence on the energization of said generator when 39thspeed thereof cor-responds to full load thereon and being effective inresponse to higher generator speeds to cause a variable influence on theenergization of said generator. I I

10. A variable speed, constant voltage generator connected to supplyenergy to a variable load, means for driving said generator, the speedof said driving means ten'dln to vary With variation in the load on saidgenerator, and means for controlling the speed of said driving means,said controlling means comprising a diskof conductive materialmechanically connected to the shaft of said generator, and means forproducing a magnetic field through said disk which varies as the speedof said generator and Which is independent of electrical characteristicsof said generator.

11.-A generator connected to supply energy to a. variable load, meansfor driving said. generator, the speed of said driving means tending tovary With variation. in the load on saidgenerator, and means forcontrolling the speed of said driving means,

said controlling means comprising adisk of.

conductive material mechanically connected to the shaft of said drivingmeans, and means independent of the circuit of said generator forproducing a magnetic field through said disk which varies froma valueineffective to produce appreciable braking action under conditions offull load on said generator to a value sulficent to produce a maximumbraking effect under conditions of no load on said generator.

12. In combination, an electric generator including field and armaturewindings and connected to supply a variable load, means responsive to acharacteristic of the. operation or" said generator for controlling thevoltage thereof, said means exercising its controlling effect throughvariation in the effective energization due to said field \vinc ing andindependently of the load on said generator, a magnetic drag for saidgenerator, and means operative to cause said drag to exercise a breakingeffect that varies as the speed of said generator 18. In combination, avariable speed elec tric generator having means for maintaining itsvoltage substantially constant, a supply circuit connected thereto, avariable load. for

said supply circuit, a magnetic drag for said generator, and energizingmeans for said drag independent of the generator circuit for causing thebreaking effect of said drag to vary as the speed of said generator.

' 14-. In combination, a turbo-generator set comprising a turbine, and agenerator directlyconnected to the shaftof said turbine and operative ata speed dependent upon its load, a supply circuit connected to saidgenerator,

a. variable working load for said supply cir- 15. A variable speedgenerator connected to supply a variable load, and an electromagneticbrake for said generator havlng an energizing Win-ding supplied from asource v independent of the circuit of said generator and carryingcurrent that varies directly as the speed at which said generatoroperates, and means for causing said brake to be inefiective to causesubstantial braking action under conditions of normal load on saidgenerator and to be automatically rendered effective for brakingpurposes on an increase in speed of said generator corresponding to aremoval of a portion of the normal load thereon. I

16. In combination, a generator connected to supply variable load, meansfor driving said generator at a variable speed dependent upon the loadthereon, said generator having means for maintaining substantially constant a characteristic of the energy supplied thereby in spite ofvariations in the load or speed thereof, and means for controlling theload on said generator-driving means, said. controllingmeans includingan electromag netic brake having energizin means effective to'cause thebrake to exercise a retarding effect upon said driving means which.varies as the speed thereof.

17. In combination, a turbo generator set comprising a turbine and agenerator having means for maintaining substantially constant i acharacteristic of the energy supplied thereby in spite of variations inthe load thereon or the speed thereof, and means forcon'trolling theloadon said turbine, said controlling means including anelectromagneticallyactuated brake comprising a conductive diskmechanically connected to the turbine shaft and energizing meanstherefor, said means being independent of the generator circuit, andsaid controlling means being substantiah ly ineffective to causebreaking action under conditions of full load on said generator andeffective to cause a braking action that varies directly as thevariation of said load from full load value. r

18. In combination, a generator, primemover for driving said generatorand having a tendency to drive said'generator at a speed that variesdirectly as the load on the generator, an electromagnetically-actuatedbrake for said prime mover including energizing means effective to causethe production of a braking effect on said prime-mover that varies asthe speed of-said prime-mover above a predetermined value and limitssaid .speedto a safe operating value under all con-- ditions of variableload on said generator, said energizing means being independent of saidgenerator circuit.

19. A generator connected to supply a variable load, means for drivingsaid generator, the speed of said driving means tending to vary withvariations in the load of said generator, and means for controlling thespeed of said driving means so as to cause the exertion of a variablebraking effect whose substantial variations are as the speed of saiddriving means only above a definite value thereof, said controllingmeans comprising an electromagnetically actuated braking device havingenergizing means independent of the circuit of said generator.

20. In combination, an electrical generator adapted to supply a variableload, means for driving said generator, the speed of said driving meanstending to vary with variations in load thereon, means for regulatingthe voltage of said generator, said regulating means comprising a sourceof direct current whose voltage varies directly with the speed of saidgenerator for speeds of the latter only above a predetermined value, andan electromagnetically-actuated brake for said driving means, theenergizing winding of said brake being supplied from said variablevoltage direct current source.

21. In combination, an electrical generator adapted to supply a variableload,

means for driving said generator, the speed of said driving meanstending to vary with variations in load thereon, means for regulatingthe voltage of said generator, said regulating means comprising a sourceof direct current whose voltage varies directly with the speed of saidgenerator for speeds thereof only above a predetermined value, and adc-energizing winding on the field of said generator supplied from saidvariable voltage direct current source.

22. In combination, an electrical generator adapted to supply a variableload, means for driving said generator, the speed of said driving meanstending to vary with variations in loadthereon, means for regulating thevoltage of said generator, said regulating means comprising a source ofdirect current whose voltage varies directly with the speed of saidgenerator for speeds thereof only above a predetermined value, anelectromagnetically-actuated brake for said driving means, theenergizing winding of said brake being supplied from said variablevoltage source, and means responsive to said variable voltage source forexercising av check on voltage increase of said generator that varies asthe speed thereof above said predetermined value.

23. In combination, an electrical generator operable at a variable speedand adapted to supply a variable'load, means for driving said generator,and means for producing a check on voltage increase of said generatoronly above a predetermined value, said means exercising its controllingefiect through variation in the energization of the field of saidgenerator, and means for producing a braking effect on the shaft of saidgenerator which varies as the speed thereof only above a predeterminedvalue.

24:. In combination, an electrical genera tor adapted to supply avariable load, means for driving said generator, the speed of saiddriving means tending to vary with varia tions in load thereon, andmeans for regulating the voltage of said generator, said regulatingmeans comprising adirect current generator, and energizing meanstherefor ettective to produce appreciable voltage at the terminals ofsaid second generator only at speeds of said first generator above apredetermined normal operating value.

25. In combination, an electrical generator adapted to supply a variableload and comprising a main energizing winding of the self-excited typeand an auxiliary energizing winding, said. windings having differentialenergizing efiects on said genera tor, means for driving said generator,and means for causing the energization of said auxiliary winding to varyin response to a characteristic of the operation of said generator onlyabove a predetermined definite value.

26. In combination, anelectrical generator adapted to supply a variableload and comprising difi jerentially arranged energizing windings havingdifi'erential energizing effects on said generator, variable speeddriving means for said generator, an auxiliary generator for supplyingone of said differentially arranged windings, and means for causing theenergizing effects of said latter winding to vary directly as butdisproportionately to the speed of operation of said driving means.

27. In combination, an electrical generator adapted to supply a variableload and having a main field winding of the self-excited type, and meansfor controlling said generator, said controlling means comprising anauxiliary generator, and means for controlling the operation of saidauxiliary generator to cause the same to supply an electromotive forceproportional to a character- I istic of the operation of said firstgenerator,

and an auxiliary energizing winding on said first generator arranged indiiierential relation with respect to said main field winding andsupplied by said auxiliary gen erator, and additional regulating meansfor said first generator responsive to the electro' motive forceproduced by said auxiliary generator.

In testimony whereof, the signature of the inventor is affixed hereto.

JOHN J. KANE.

